Inhibitory effect of flavonoids from citrus plants on Epstein-Barr virus activation and two-stage carcinogenesis of skin tumors.

To search for possible anti-tumor promoters, thirteen flavones (1-13) obtained from the peel of Citrus plants were examined for their inhibitory effects on the Epstein-Barr virus early antigen (EBV-EA) activation by a short-term in vitro assay. Of these flavones, 3,5,6,7,8,3',4'-heptamethoxyflavone (HPT) (13) exhibited significant inhibitory effects on the EBV-EA activation induced by the tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA). Further, compound 13 exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.

HL-60 differentiating activity and flavonoid content of the readily extractable fraction prepared from citrus juices.

Citrus plants are rich sources of various bioactive flavonoids. To eliminate masking effects caused by hesperidin, naringin, and neoeriocitrin, the abundant flavonoid glycosides which make up 90% of the conventionally prepared sample, the readily extractable fraction from Citrus juice was prepared by adsorbing on HP-20 resin and eluting with EtOH and acetone from the resin and was subjected to HL-60 differentiation assay and quantitative analysis of major flavonoids. Screening of 34 Citrus juices indicated that King (C. nobilis) had a potent activity for inducing differentiation of HL-60, and the active principles were isolated and identified as four polymethoxylated flavonoids, namely, nobiletin, 3,3',4',5,6,7, 8-heptamethoxyflavone, natsudaidain, and tangeretin. HPLC analysis of the readily extractable fraction also indicated that King contained high amounts of these polymethoxylated flavonoids among the Citrus juices examined. Principal component and cluster analyses of the readily extractable flavonoids indicated peculiarities of King and Bergamot.

Inhibitory effect of Epstein-Barr virus activation by Citrus fruits, a cancer chemopreventor.

To search useful compounds in Citrus fruit for cancer chemoprevention, we carried out a primary screening of extracts of fruit peels and seeds from 78 species of the genus Citrus and those from two Fortunella and one Poncirus species, which were closely related to the genus Citrus. These Citrus extracts inhibited the Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) as a useful screening method for anti-tumor promoters. Our results indicated that Citrus containing substances may be inhibit susceptibility factors involved in the events leading to the development of cancer.

Calcium Dependence of Settlement and Nematocyst Discharge in Actinulae of the Hydroid Tubularia mesembryanthemum.

The influence of Ca2+ and Mg2+ ions on both atrichous isorhiza (AI) discharge and settlement of actinular larvae of the hydroid Tubularia mesembryanthemum was investigated. Mg2+-supplemented artificial seawater (ASW) completely inhibited both events at a concentration of 206 mM, whereas lowered Mg2+ concentrations enhanced them. Ca2+ ions in the bathing solution highly regulated AI discharge and settlement, and Mg2+ ions may down-regulate these events. The effect of inorganic Ca2+-channel blockers, including Gd3+ and La3+, was also examined. Larval settlement was inhibited by Co2+, Ni2+, Cd2+, La3+, and Gd3+, with half inhibitory concentrations (IC50) of 5800, 260, 53, 45, and 7 {mu}M, respectively; AI discharge was also inhibited by these ions, with IC50 values of 6600, 500, 78, 41, and 5 {mu}M, respectively. These results suggest possible involvement of stretch-activated Ca2+ channels in the signal transmission of both AI discharge and larval settlement.